Many patients receive care in an intensive care unit or similar setting following surgery, injury, trauma, or acute medical illness. At some time in their disease course they may suffer from dysfunction or failure of one or more organ systems. Although some patients succumb from their illness and die, most eventually recover, albeit after a prolonged duration of hospitalization.
Decisions must be made about whether and when patients are ready for a normalization (or accelerated normalization) of their care. Several types of common clinical problems are exemplified below:
Initiation of Enteral Feeding
Enteral feeding, i.e. instilling food into the stomach or intestines via a feeding tube or the mouth, is beneficial to some patients but deleterious to those patients whose gastrointestinal perfusion and function is suboptimal. Failures in enteral feeding can be classified as either xe2x80x9cunderfeedingxe2x80x9d or xe2x80x9coverfeedingxe2x80x9d. Underfeeding results when a critically ill patient is either not started on enteral feeds or else is administered suboptimal calories. Underfeeding can result in malnutrition and its associated complications (e.g. infections, low colloid oncotic pressure) which results in a prolongation of the duration of ICU stay and hospitalization. Overfeeding, in contrast, results when a patient is enterally fed but the patient""s gastrointestinal tract (or overall circulatory system) is not yet healthy enough to tolerate the increased stress of enteral feeding. Overfeeding can result in vomiting and aspiration of enteral feeds into the lungs leading to aspiration pneumonitis/pneumonia. Overfeeding can also lead to ileus, fever, and abdominal tenderness which can mimic other serious disorders such as abdominal abscess/infection, and dead bowel. It can be difficult to predict a priori which patients will tolerate enteral feeding.
Weaning from Mechanical Ventilation
Mechanical ventilation is used to support adequate oxygenation and ventilation in patients with pulmonary dysfunction. Providing mechanical ventilation to a patient when it is not necessary can lead to recognized complications such as muscle weakness and aspiration pneumonia and results in increased hospital length of stay. Discontinuing or weaning mechanical ventilation in a patient prematurely can lead to complications such as pulmonary failure, intestinal dysfunction, cardiac arrhythmias, and a general setback in the patient""s recovery. It can be difficult to predict a priori whether patients require more or less ventilatory support.
Weaning of Vasoactive Medications
Vasoactive agents such as epinephrine, dobutamine, dopamine, norepinephrine, and milrinone are commonly administered to critically ill patients in order to insure adequate perfusion of vital organs. Unnecessary administration of these agents can result in prolonged hospitalization and the risk of complications such as cardiac arrhythmias. In contrast, insufficient administration of these agents can result in inadequate organ perfusion which can result in organ dysfunction and death. It can be difficult to determine if and how rapidly vasoactive agents can be weaned. It is also difficult to determine if circulatory support with vagoactive agents should be increased.
The present invention is a method of guiding the care of a critically ill patient or other high risk patient in which the response of gastric juice pH to an effective dose of a gastric acid stimulant or suppressant agent is used. Preferably the agent is a stimulant. A patient who demonstrates a significant change in the gastric juice pH using this test can have their medical care normalized in an accelerated fashion thereby reducing the duration, intensity, and cost of their hospital care. Conversely, a patient who fails to respond is not ready for normalization of care and may require an increased level of care. The invention provides a single objective test which simplifies care decisions.
The invention also features kits for guiding care of an acutely ill or high risk patient. The kits include at least one effective dose of a gastric acid stimulant or suppressant agent and apparatus providing access to the patient""s gastric juice pH, such as a disposable gastric pH probe. Preferably the agent is a stimulant.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments.
A method of guiding the care of a critically ill patient or other high risk patient, said method comprising administering an effective dose of a gastric acid stimulant or suppressant agent and then measuring for an acute change in the gastric juice pH. The ability of the gastric cells to respond to this pharmacological challenge is a good indicator of the perfusion and function of the gastrointestinal tract. In contrast to the prior art which has described a pharmacological test for use in the diagnoses of chronic illnesses and rare endocrine disorders, this invention relates to the use of this challenge test to guide the care of patients with acute critical illness. Surprisingly, this test allows for the monitoring of organs unrelated to gastric acid secretion or suppression per se.
Target Population
Any patient with acute illness may benefit from this invention. Patients who are receiving care in an intensive care unit or similar setting following surgery, injury, trauma, or acute medical illness are likely candidates. In particular, patients with acute organ failure are at risk for inadequate gastrointestinal perfusion and dysfunction and are candidates for use of this method. Patients in whom decisions need to be made regarding either initiating or weaning enteral feeding, vasoactive agents, and/or mechanical ventilation may benefit from the use of the method described herein. The patients face acute medical situations, in which their condition may be changing and appropriate changes in medical treatment may be required.
Uses
Some of the uses of this test include assessing gastrointestinal perfusion and function in order to (among other things):
A. Guide the decision to extubate and/or wean a patient from mechanical ventilation (i.e. decrease ventilating support); or to increase ventilating support
B. Guide the decision to initiate, increase, terminate, or wean enteral feeding;
C. Guide the decision to initiate, increase, terminate, or wean vasoactive agents.
Pharmacological Challenge Agents
It is preferable to use a gastric acid stimulant if the baseline gastric juice pH is greater than 2.0. It is preferable to use a gastric acid suppressant if the baseline gastric juice pH is less than 2.0. A positive signal is typically manifested by a change in several pH units from the baseline value although a change of 1.0 pH units in response to the challenge agent is usually indicative of a positive signal. Most patients respond in a clear way to the challenge which reduces ambiguity in the interpretation of the results. In the event of an ambiguous test in a patient with a baseline pH of 2-3, it may be useful to repeat the test using the opposite pharmacological agent. For example, if pentagastrin is initially used and yields a negative response it may be useful to subsequently conduct a challenge test with omeprazole, preferably allowing at least 1-3 hours in between tests. A pharmacological challenge is typically conducted once every 1-3 days, although more frequent measurements can be made if deemed useful. If the patient is receiving enteral nutrition it may be preferable to discontinue feeding for several hours (e.g. 4 hrs.) prior to a pharmacological challenge.
Although any type of gastric acid stimulant can be used, the preferred agent is pentagastrin, a commercially available agent. Pentagastrin is a synthetic pentapetide that contains the carboxyl terminal tetrapeptide responsible for the actions of natural gastrins and its most prominent action is in the stimulation of gastric acid secretion. Pentagastrin stimulates gastric acid secretion approximately 10 minutes after subcutaneous injection with peak response occurring in most cases 20-30 minutes after administration. The duration of activity is usually between 60-80 minutes. Pentagastrin has a short half life of approximately 10 minutes. The preferred route of administration is subcutaneous although any alternative route, e.g. intravenous, may be acceptable. Any dose which has no significant side effects and is effective at stimulating gastric acid secretion can be used. The typical dose of pentagastrin is 6 micrograms/kg for subcutaneous administration.
Any acute acting gastric acid suppressant can be used. Example of useful gastric acid suppressants include proton pump inhibitors (e.g. omeprazole) and histamine H2 receptor antagonists (e.g. ranitidine). Proton pump inhibitors may be preferable given their direct mechanism of action. The preferred dosage and route of administration for the gastric acid suppressant will be relatively free of side effects and result in a significant pharmacological effect within 1 hour of administration. Examples of doses include omeprazole (80 mg intravenous) or ranitidine (50 mg intravenous).
Measurement of Gastric Juice pH
Any accurate method of measuring gastric juice pH may be used in this test. A method is preferable if it is easy to use, inexpensive, and relatively non-invasive and free of side effects. A preferred method involves the use of a pH measuring device that is encapsulated into the distal end of a standard 18 French tube that is inserted into the gastric lumen either through the mouth or nose. This tube would allow for the drainage of stomach contents, if necessary for other medical reasons, and administration of enteral feeds into the stomach, if feeding is deemed to be warranted. An example of such a tube is the GrapHprobe(trademark) (Zinetics Medical, Utah, USA). A graphometer pH meter (e.g. Zynetics Medical, Utah, USA) can be connected to the sensor. This unit has a liquid crystal display and produces a measurement of gastric juice pH accurate to 0.1 pH unit. Alternative manufacturers of pH containing probes and pH monitors can be used.